If your dog thinks of himself as being, well, the top dog, then you'll likely know it by his actions -- think charging past you in the hallway or barking at you to do something. On the other hand, if he's submissive and thinks that you're the head honcho, you'll probably know that, too. Licking is frequently an indication of feelings of submission in doggie land.
Dogs are descendants of wolves, and as a result naturally adopt similar behaviors when it comes to interactions with their family members and peers. In the canine world, single "alpha dogs" pave the way for the rest of their packs. The rest of the members of the pack are generally submissive and humble to the leader. They know the situation and know their social status. As household pets, dogs often think of their owners as being their "alpha dogs." If they perceive themselves as being the leaders of their owners, however, it could lead to dominance, lack of respect and general behavior problems.
One classic sign of submission in canines is facial licking. If your pooch enthusiastically begins licking your face after you arrive home, sure, he loves you, but at the same time he also might be communicating something a little deeper than that, which could be something like "I am fully aware of the fact that you're in charge of me. I also accept it happily." Pooches don't limit this face licking to their interactions with their owners. They sometimes even do it when they encounter other dogs they consider to be stronger and more powerful.
Other Clues of Submission
Licking isn't the only way that dogs express their submission. They also do so by crouching their bodies down, going on their backs and showing their stomachs, tucking their tails into their hind legs, abstaining from looking at others straight in the eyes and pushing their ears down. Some dogs, especially young puppies, might even accidentally wet themselves out of submission, especially if they feel nervous or frightened for any reason. This kind of submissive behavior, especially in adult animals, sometimes signifies a past of stress or neglect. It definitely is worth exploring, through a combination of socialization, training and close veterinary guidance.
Other Possible Causes for Licking
Licking doesn't necessarily have to be a sign of submission in dogs. It can sometimes mean something as simple as that your dog enjoys the slightly salty flavoring of your hands -- maybe you were just munching on potato chips and he can taste it. It can sometimes even be as simple as tedium. The little guy is bored and licking on people passes the time better than staring off into space. If he's licking himself rather than you or anyone else, it can sometimes hint to medical issues such as skin allergies. If that's the case, it's time to pencil in a veterinary appointment and figure out the specific cause.